a) Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device including a dry-etching process for forming a connection (contact) hole through an insulating film.
b) Description of the Related Art
In a semiconductor device having a multi-layer wiring structure, insulation between wiring layers is made by an interlayer insulating film. In order to form electrical connection between the wiring layers, a connection (contact) hole is formed through the interlayer insulating film by using a resist pattern. Anisotropic etching or a combination of isotropic etching and anisotropic etching is performed to retain a high patterning precision. For anisotropic etching of an interlayer insulating film, fluorine containing etching gas is used such as CF.sub.4, CHF.sub.3, C.sub.2 F.sub.6, C.sub.3 F.sub.8, and C.sub.4 F.sub.8. After the connection hole is formed, the resist pattern is removed.
A residue called a crown may be left in a connection hole after the connection hole forming process. If the succeeding process is performed with the crown being left in the connection hole, a manufacture yield and reliability may be lowered. Various methods have been proposed to remove a crown.
A method proposed in JP-A-6-37188 ashes (half-ashes) a portion of resist on an aluminum wiring layer and thereafter removes the remaining resist and crown at the same time by using fuming nitric acid.
However, if this method is used for ashing resist on a laminated wiring structure including an aluminum or aluminum alloy layer and a cap layer made of Ti compound or the like formed on the aluminum or aluminum alloy layer, the cap layer is removed by nitric acid.
JP-A-6-77178 proposes a method of manufacturing a semiconductor device having an aluminum alloy layer and a TiON antireflection layer laminated on the aluminum alloy layer, capable of facilitating to remove a crown.
With this method, in forming a connection hole through an interlayer insulating film to an aluminum alloy layer, by using a resist pattern, etching is temporarily stopped when the connection hole is formed to an intermediate depth of the insulating film. After the side wall of the resist pattern is retracted through ashing with oxygen plasma, the etching is again performed. Since a re-deposition layer formed on the side walls of the resist pattern and connection hole can be separated, it becomes easy to remove the re-deposition layer by nitric acid or the like.
However, since the side wall of the resist pattern is retracted during the etching process, the etching precision lowers. Even if the TiON antireflection film on the aluminum alloy layer is to be left, the TiON antireflection film may be removed while the re-deposition layer is removed with nitric acid. This problem also occurs if a cap layer of Ti compound is formed on an aluminum alloy layer.
A method proposed in JP-A-7-99188 etches an interlayer insulating film by adding nitrogen to a gas not containing O.sub.2 to form a connection hole through the interlayer insulating film to an aluminum alloy layer.
Even if aluminum is sputtered and re-deposited on the side wall of a resist pattern, the re-deposition layer can be prevented from being cured. After etching, nitric acid rinsing and water rinsing are performed.
However, if this method is used for a wiring structure including an aluminum alloy layer and a cap layer of Ti alloy formed thereon, the cap layer may be removed by nitric acid.
As described above, if a crown formed when a connection hole is etched through an insulating layer to a wiring layer, is removed by using conventional techniques, the wiring layer is likely to be affected.